Plastisol

Plastisol is a suspension of PVC or other polymer particles in a liquid plasticizer; it flows as a liquid and can be poured into a heated mold.  Aside from molding, plastisol is commonly used as a textile ink for screen-printing.

• Screen printing is a printing technique where a mesh is used to transfer ink onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mesh apertures with ink, and a reverse stroke then causes the screen to touch the substrate momentarily along a line of contact. This causes the ink to wet the substrate and be pulled out of the mesh apertures as the screen springs back after the blade has passed. One color is printed at a time, so several screens can be used to produce a multicolored image or design.

Plastisol is used as ink for screen-printing on to textiles. Plastisols are the most commonly used inks for printing designs on to garments, and are particularly useful for printing opaque graphics on dark fabrics.

Plastisol inks will not dry on their own, but must be cured.

• Curing can be done with a flash dryer, or any oven. Most plastisols need to reach a temperature of about 180 degrees Celsius (350 Fahrenheit) for full curing.

Plastisol tends to sit atop the fabric instead of soaking into the fibers, giving the print a raised, plasticized texture.  Unfortunately, this method does not provide the best hands to the fabric.  Other inks can produce a softer feel.

The next time someone asks you, "what is plastisol?", we hope you now have an answer for them.

An Ink That Waits for Heat

Plastisol behaves unlike ordinary ink from the moment it is mixed. As a suspension of PVC or other polymer particles in a liquid plasticizer, it flows as a liquid, can be poured, and stays workable on the screen without drying in the mesh the way water-based inks can. That stability is a production advantage: a printer can leave plastisol on a press, print a run, and return to the same ink without it having skinned over or clogged the stencil. The trade-off comes at the end of the run, because plastisol inks will not dry on their own and must be cured. Curing can be done with a flash dryer or any oven, and most plastisols need to reach a temperature of about 180 degrees Celsius, or 350 Fahrenheit, for full curing, at which point the particles and plasticizer fuse into a solid, durable film bonded to the garment.

An undercured print is the characteristic plastisol fault: the surface may feel dry while the interior of the ink film remains unfused, so the design cracks or washes out early in the garment's life. Correct curing is therefore a measured step, not a guess, and print shops check dryer temperature and dwell time against the ink manufacturer's specification for the fabric being printed. Because the ink film is fused plastic, a properly cured plastisol print resists washing and abrasion well, which is one reason plastisols became the most commonly used inks for printing designs onto garments in commercial screen printing.

Printing One Color at a Time

Screen printing itself is a stencil process: a mesh is used to transfer ink onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mesh apertures with ink, and a reverse stroke then causes the screen to touch the substrate momentarily along a line of contact, so the ink wets the substrate and is pulled out of the mesh apertures as the screen springs back after the blade has passed. One color is printed at a time, so several screens can be used to produce a multicolored image or design, each screen carrying one color's part of the artwork and registering against the others.

Plastisol suits this process on garments for a specific visual reason: opacity. Plastisols are particularly useful for printing opaque graphics on dark fabrics, because the ink film sits on top of the cloth and covers the garment color beneath it, letting a bright design hold its color on a black or navy shirt without a heavy underbase in many cases. The same quality creates the method's known drawback. Because plastisol tends to sit atop the fabric instead of soaking into the fibers, it gives the print a raised, plasticized texture, and this method does not provide the best hand to the fabric; other inks can produce a softer feel. Printers therefore choose plastisol deliberately — for opacity, durability, bright color and ease of handling — and accept a firmer print surface as the price, or select a softer ink system when the feel of the finished shirt matters more than coverage.